Object seems split into two
Your mesh is a nightmare to edit, because you applied the SubSurf modifier. You shouldn't do that unless you've got a good reason !
So first, we will Un-subdivide it. You can add a Decimate modifier, select the Un-Subdivide mode, and choose a Iteration of 10. Feel free to play with that value, 10 looks like a good compromise :

You can now Apply this modifier ; this way, you'll get a mesh that is largely easier to Edit.

The next step is to add a Subdivision modifier again, so the mesh will look smoother. A Level of 2 or 3 is more than enough.
For the mesh to look even smoother, but without adding more faces, you can go in the Object menu and select Shade Smooth.

There is still some pinches, but now you can move vertices in Edit Mode to mitigate them. Anyway due to the bad topology on the highlighted zone, you won't have a perfect result :

I would suggest to read this Topology Guide (the whole site is quite interesting) if you want to improve this useful skill.